A key feature of the approach - coined `shape-from-video'
- is that the necessary camera calibration is carried out automatically,
from the same image data that is used for the generation of the
3D reconstructions. Hence, the sole input that this approach needs
are images. No knowledge is necessary about the camera settings
or about the relative positions from where images are taken.
A first example is one of the Dionysos statues
found in Sagalassos. In antiquity, this 2m high statue was placed
on the monumental fountain (nymphaeum) situated at the upper market
square of Sagalassos. The statue is now located in the garden of
the museum in Burdur. Producing the 3D reconstruction only required
the recording of a 1-minute video. Bringing in special equipment
such as a laser range scanner would not only have been logistically
more demanding, it would also have required a special authorisation.
In Figure 1 different steps of the reconstruction process are illustrated.
The 3D model was obtained from a single depth map. A more complete
and accurate model could be obtained by combining multiple depth
maps. A smoother look for the shaded model could be obtained by
filtering the 3D mesh in accordance with the standard deviations
that are obtained as a by-product of the depth computation. This
is not so important when the model is texture mapped with the original
images. For many visualisation purposes, this result will suffice.
Figure 1: 3D reconstruction of Dionysos. (a) one
of the original video frames, (b) corresponding depth map, (c) shaded
view of the 3D reconstruction, (d) view of the textured 3D model.
A second example is shown in Figure 2. It is a Medusa head which
is located on the entablature of the fountain building. The head
itself is about 30cm large. The 3D model was obtained from a short
video sequence. In this case a single depth map was also used to
reconstruct the 3D model. Notice that realistic views can be rendered
from viewpoints that are very different from the original viewpoint.
reconstruction of a Medusa head. (a) one of the original video frames,
(b) corresponding depth map, (c) and (d) two views of the 3D model.
An important advantage of our approach is its ease-of-use. Taking
images is part of regular, archaeological practice. The ability
to turn normal photographs into 3D models literally adds a new dimension
to archaeological records. Compared to non-image based techniques
there is the important advantage that surface texture is directly
extracted from the images. This
adds to the realism and authenticity of the reconstructions. A disadvantage
of the approach (and more in general of most image-based approaches)
is that it does not directly capture the photometric properties
of an object, but
only their combination with lighting. It is therefore not possible
to render the 3D model under different lighting. Recent work (e.g.
by Debevec et al.,USC) does allow to change the lighting for archaeological
artefacts. There an image-based approach is also used. But in that
case, use is made of a controlled lighting set-up during acquisition.
It remains to be investigated what can be done in uncontrolled lighting
environments like ours.
As many of the bigger archaeological objects
and scenes do not lend themselves to be captured in one continuous
image sequence, a new tool (‘the Layer Matcher’) has
been developed that allows for the merging of different 3D reconstructed
parts of the same scene in one single framework. This is accomplished
by querying the user for some corresponding points between the different
reconstructions. This tool demonstrated to be especially useful
for the generation of 3D data for stratigraphical layers. It seems
to be difficult to capture an entire layer with a single image sequence.
The next figure shows how two 3D reconstructions, originating from
separate image sequences, are merged together into a single framework
by indicating some corresponding points between both reconstructions.
Figure: Top: Two 3D reconstructed parts of
the same stratigraphic layer originating from two separate image
sequences. Bottom: The merged result of both reconstruction into
a single framework after indication of some corresponding points
in both reconstructions (red points in top figures).
Another feature of the ‘Layer Matcher’
is the ability to merge 3D reconstructions of consecutive stratigrahical
layers as the archaeologists progress and uncover new stratigraphical
layers, thereby destroying the old layers. The tool makes it possible
to keep a 3D record of all layers in time, a valuable advantage
due to the destructive nature of the excavation of stratigraphic
layers. The next figure demonstrates how two consecutive layers
(in time) can be merged together to give an impression of the excavation
Figure: Top: Two reconstructions of the same
area at different times. The left layer is destroyed to uncover
the right layer. Bottom: The integration of both reconstructions.
The top layer appears to be floating above the bottom layer. This
gives an impression of the excavation activity between two time